1. Field of the Invention
This invention relates generally to auditory diagnosis and assistance and more particularly, but not by way of limitation, to an at least partially implantable hearing assistance system providing middle ear vibrations and sensing particularly based on evoked otovibratory and otoacoustic emissions.
2. Description of Related Art
Some types of partial middle ear implantable (P-MEI), total middle ear implantable (T-MEI), cochlear implant, or other hearing assistance systems utilize devices disposed within the middle ear or inner ear regions. Such devices might include an input transducer for receiving sound vibrations or an output stimulator for providing mechanical or electrical output stimuli corresponding to the received sound vibrations.
An example of such a device is disclosed in U.S. Pat. No. 4,729,366, issued to D. W. Schaefer on Mar. 8, 1988. In the ""366 patent, a mechanical-to-electrical piezoelectric input transducer is associated with the malleus, transducing mechanical energy into an electrical signal, which is amplified and further processed by an electronics unit. A resulting electrical signal is provided to an electrical-to-mechanical piezoelectric output transducer that generates a mechanical vibration coupled to an element of the ossicular chain or to the oval window or round window for assisting hearing. In the ""366 patent, the ossicular chain is interrupted by removal of the incus. Removal of the incus prevents the mechanical vibrations delivered by the piezoelectric output transducer from mechanically feeding back to the piezoelectric input transducer.
Introducing devices into the middle or inner ear regions typically involves intricate surgical procedures for positioning or affixing the devices and its components for communication or coupling to the desired auditory elements. The proper positioning and affixation for obtaining the best input signal and providing the best output stimuli is a often a difficult task. The patient is typically under general anesthesia, and is thus unable to provide the implanting physician with any human feedback or information regarding how well sound is being perceived. Thus, the implanting surgeon faces a difficult task that may yield uneven results in the proper positioning and affixation of components in the middle or inner ear regions in order to obtain proper sound perception. There is a need in the art to facilitate optimal positioning and affixing components in the middle or inner ear regions in order to obtain proper sound perception. After implantation, the physician would like to diagnose malfunctions of the hearing assistance system without performing further invasive procedures. It is possible for an implanted device or component to become dissociated from its corresponding auditory element (e.g., by a severe blow to the head or otherwise). Further, changes in one or more of the ossicular chain elements may result in the displacement and misalignment of the device or its components. For example, an output transducer initially positioned to be in contact with the stapes may later become dissociated from the stapes. There is, therefore, a need in the art to enable a physician to determine, without surgical intervention, whether or not the output transducer or other implanted component is still properly positioned.
Other complicating factors are also present. There may be a large variation between patients in the sound perception characteristics of their auditory systems. Moreover, there may be variations between hearing assistance systems, such as in their component characteristics. For example, the characteristics of the input transducer and output stimulator may well vary to some degree. Accordingly, there is a need for hearing assistance systems to provide diagnostic or calibration information to the physician, such as during or after the surgical implantation procedure, in order to ascertain efficacy and adjust therapy accordingly. There is a further need for self-calibration of such hearing assistance systems to increase their ease of use.
In the unrelated technological field of audiometric screening and diagnosis, numerous audiometric screening techniques have been developed to assess the state of a patient""s auditory system. Some of these techniques are designed to provide diagnostic information without active participation by the patient. Such techniques are particularly useful for sleeping, anesthetized, unconscious patients or newborn infants who lack the cognitive ability to provide feedback to the physician. One such technique involves detection of transient evoked otoacoustic emissions, also referred to as Kemp echoes, cochlear echoes, and delayed evoked otoacoustic emissions.
In order to perform clinical diagnosis using otoacoustic emissions, a brief acoustic (i.e., sound pressure wave) stimulus is provided by an earphone that is introduced into the external auditory canal. Evoked otoacoustic emissions are sounds generated within the normal inner ear (cochlea) in response to the acoustic stimulus after a 5-20 millisecond latency period. Resulting sound pressure waves corresponding to the evoked otacoustic emissions are detected by a microphone introduced into the external auditory canal. Responses to several stimuli are averaged, amplified, and filtered. Transient evoked otoacoustic emissions are measurable in normal-hearing persons. However, if hearing loss exceeds 40-50 dB, an otoacoustic emission typically cannot be evoked in response to a transient stimulus. As a result, the presence or absence of transient evoked otoacoustic emissions can be used as an audiometric screening tool.
However, using transient evoked otoacoustic emission as a clinical diagnostic tool presents numerous difficulties. One such problem results from spontaneous otoacoustic emissions, which are internal sounds emitted by the human ear even in the absence of an external stimulus. The presence of such spontaneous otoacoustic emissions can make the transient evoked otoacoustic emissions more difficult to detect. Another problem is presence of noise in the introduced acoustic stimulus and the detected acoustic response. Such noise includes electronic noise (e.g., from the microphone, preamplifiers, receiver, filters, etc.), body noise (including spontaneous otoacoustic emissions), and environmental acoustic noise that enters the external auditory canal. This type of noise sources tend to mask the evoked otoacoustic emission, making it more difficult to detect. Thus, there is a need in the art to improve the sensitivity of detecting transient evoked otoacoustic emissions. For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need for calibration and diagnostic capability of PMEI, T-MEI or other hearing assistance systems, and there is a need in the unrelated technological field of audiometric screening and diagnosis for improved techniques of detecting cochlear emissions such as transient evoked otoacoustic emissions.
The present invention provides techniques for detecting cochlear emissions and performing audiometric, calibration, and diagnostic functions in an at least-partially implantable hearing assistance system. The present invention facilitates the optimal orientation, positioning and affixing of hearing assistance system devices and components in the middle or inner ear regions to ensure proper sound perception. According to one aspect of the present invention, a physician can determine, without surgical intervention, whether or not an already-implanted component is still properly positioned. Another advantage of the present invention allows improved sensitivity detection of cochlear emissions.
In one embodiment, the invention provides a transducer adapted for sensing mechanical vibrations produced by an inner ear. In another embodiment, the invention provides an apparatus comprising an output transducer and a first input transducer. The output transducer is adapted for coupling a mechanical vibration output stimulus to an inner ear in response to an electrical output signal. The first input transducer is adapted for receiving an emission (e.g., transient evoked otovibratory or otoacoustic emission) from the inner ear and generating an electrical first input signal in response to the emission. The output and first input transducers can be integrally or separately formed.
In one embodiment, the apparatus includes an electronics unit that is capable of adjusting the electrical output signal based on the received electrical first input signal. In another embodiment, the apparatus includes a second input transducer. In yet another embodiment, the apparatus further comprises an external transceiver, adapted for communication with the electronics unit.
Another aspect of the invention provides a method that includes disposing a transducer in the middle ear, stimulating the inner ear using the transducer disposed in the middle ear, and sensing emissions (e.g., transient evoked otovibratory or otoacoustic emissions) from the inner ear in response to stimulating the inner ear.
In one embodiment, the method also includes programming a hearing assistance device based on the sensed emissions from the inner ear. Another embodiment includes adjusting the stimulation of the inner ear based on the sensed emissions from the inner ear. In yet another embodiment, a data signal, based on the sensed emissions from the inner ear, is stored, or communicated from an implanted transmitter to an external receiver. A further embodiment includes repositioning the transducer (or adjusting a contact force between the transducer and an auditory element) based on the sensed emissions from the inner ear. The invention also allows programming of hearing assistance signal processing parameters of an implantable hearing assistance device based on the sensed emissions from the inner ear.
Another aspect of the invention provides a method that includes stimulating the inner ear, sensing emissions from the inner ear in response to stimulating the inner ear, and programming an implantable device (e.g., adjusting a gain or frequency response) based on the sensed emissions from the inner ear.
As described below, the present invention allows improved sensitivity detection of cochlear emissions, and provides easier implantation and subsequent calibration, diagnostic, and audiometric functions of an implantable hearing assistance device.